Explosive line wave generator



United States Patent O Claims. (Cl. E32- 22) The invention described herein was made in the course of, or under, Contract W-7405-ENG-48 with the United States Atomic Energy Commission.

The present invention relates to high explosives and more particularly to high explosive sheet line wave generators.

The use of line wave generators to simultaneously initiate a high explosive charge at various points or along a line is extensively employed in the arts of hardening, joining and severing of metals. Such uses are described in the U.S. Patents No. 2,605,704 (Jacques Dumas, August 5, 1952) and No. 2,367,206 (C. O. Davis, January 16, 1945). Line wave generators suitable for these applications are described in U.S. Patents No. 2,943,571 (D. L. Coursen, July 5, 1960) and No. 2,774,306 (N. A. McLeod, December 18, 1956). Generally these line wave generators comprise a flat explosive body having at least one terminal edge of a size and shape conforming to a desired detonation front and a predetermined point for igniting the explosive. Generally, the explosive body has a series of apertures cut therein to control the propagation of the detonation wave front from the initiation point to the terminal edge. The apertures are distributed and shaped in accordance with the nature of the terminal edge. In general, the explosive sheet is a maze in which the path length between the ignition point and any point on the terminal edge is constant. The detonation wave front emanating lfrom the point of ignition is cotinuously deformed or diverted by the apertures causing the detonation front to reach the terminal edge simultaneously at all points.

In many applications of line wave generators, e.g. shockwave amplification -by coherent focussing, it is necessary that the detonation front arrive at the terminal edge with a simultaneity in the range of 10J? to 10-8 seconds. However, due to the construction of prior art apertured line wave generators, the arrival of the detonation front at the terminal edge is limited to a simultaneity in the range of 10 to 100 microseconds at best. Furthermore, such line wave generators are incapable of producing a smooth detonation front because a -detonation frontlet traveling between adjacent apertures develops a secondary curvature due to the propagation velocity of the frontlet being smaller at the boundary of the apertures. Prior to arrival at the terminal edge of the explosive body, the detonation frontlets merge into an integral, however, scalloped detonation front. The secondary curvature of the frontlets is retained forming a ripple which limits the degree of simultaneity.

Another disadvantage of apertured line wave generators of the prior art is their relative infiexibility, i.e., the limited variety of different geometries to which the terminal edge may be fitted without a significant loss of simultaneity. The reason for the limited exibility of the prior art line generators is that the detonation velocity varies with strain and deformation of the explosive sheet. Therefore the use of apertured prior art explosive line generator has been limited to the ignition of a limited group of closely related geometric shapes.

Moreover, the preparation of apertured line wave generators may involve as much as 30% Wastage of the explosive sheet in the form of cutaway apertures.

Accordingly, it is an object of the present invention 3,242,863 Patented Mar. 29, 1966 lCC to provide a line wave generator furnishing a detonation front simultaneously incident along a line in an interval of less than 10-7 seconds.

Another object of the present invention is to provide a line wave generator having a flexible terminal edge which can be deformed into a multiplicity of geometrical shapes while maintaining a relatively high degree of simultaneity of arrival of the detonation front at the terminal edge.

Still another object of the present invention is to provide a line wave generator having a geometrical configuration which may be formed with minimal explosive wastage.

Other objects and advantages of the line wave generator will become apparent upon consideration of the following description in conjunction with the drawings, in which:

FIGURE 1 represents a preferred embodiment of the line Wave generator of the present invention; and

FIGURE 2 illustrates the preferred embodiment disposed to generate a straight line -detonation front.

In general the line wave or detonation front generator of the invention is provided as a circular sector of a sheet of flexible high explosive composition which is ignited in the region of the apex and in which the detonation front propagates radially to emerge uniformly along the arcuate -or circular terminal boundary. To obtain the uniform time of arrival, i.e., simultaneity, at the locus, the sectored explosive sheet is pierced or slit to provide a plurality of sets of radial cuts, the cuts of each set being preferably of uniform lengths, however, with the cuts of different sets being of different controlled lengths and with said cuts beginning in a region in proximity to said terminal arcuate boundary, and extending .radially towards said apex. Moreover, the cuts of each set are interposed in regular sequence 4between the cuts of a set of relatively longer length so that the cuts of each set terminate inwardly of the terminal boundary substantially along a circular arc inscribed from said apex. Accordingly, the inner termini of said sets of cuts lie along a series of concentric arcs and the radial cuts or slits divide the sectored sheet of explosive into a series of sectored segments or zones disposed between the aforesaid concentric arcs. Preferably, the spacing of said radial cuts is uni-form i.e., equal distant so that said zones are of equivalent areas. As used herein, to pierce means to cut said explosive sheet without any substantial removal of material.

More particularly, referring to FIGURES 1 and 2 the line Wave generator of the present invention comprises a circular sector of a exible explosive sheet 11 which may range from at least fractions of a millimeter to several centimeters in thickness. A preferred explosive sheet material for the present line generator comprises an organic nitrate or nitramine in a binder matrix comprising a rubber and a terpene hydrocarbon resin. 'This preferred explosive is disclosed in detail in U.S. Patent No. 2,999,743, issued to C. J. Bresa and C. O. Davis on July 5, 1960. A typical sheet explosive is marketed by E. I. du Pont de Nemours & Company, under the designation FIL-506 flexible sheet explosive. Other sheet or film high explosive compositions can be used in practicing the present invention. To attain high degrees of simultaneity it is requisite that the explosive sheet be flexible and of a uniform thickness and composition. It is to be realized that where lesser degrees of simultaneity are appropriate, the uniformity requirements can be reiaxed somewhat.

Sheet 11. is pierced by a rst set of spaced radial cuts 12 beginning near the apex 13 and terminating in proximity to the terminal arcuate edge 14 defined by the cir- HW l.

f., L5 cular periphery of sheet 11. For most advantageous operation radial cuts 12 are equally spaced apart whereby explosive sheet 11 is radially partitioned into a number of equal radial zones. A second set of radial cuts 16, preferably shorter than cuts 12 and terminating in proximity to terminal edge 14, bisect the aforementioned radial zones. A third and fourth set of radial cuts 17 and 18 respectively, preferably cuts 18 shorter than cuts 17 and cuts 17 shorter than cuts 16, pierce sheet 11 to bisect the radial zones defined by the next larger set of cuts. The third and fourth set of radial cuts, 17 and 18 respectively, terminate in proximity to the terminal edge To initiate the line generator, the butt end of an initiator (not shown), such as an electric blasting cap containing lead styphnate, pentaerythritol tetranitrate or RDX explosive, is secured to the apex 13 of the line generator and is ignited in the usual manner. Upon ignition, a detentation front is generated and travels toward the terminal edge 14 and reaches all portions thereof simultaneously. By virtue of the radial cuts the terminal edge can be fiexed to produce a ystraight or curved line contact with flat or curved surfaces of a wide variety and particularly into a straight line by humping the radial zones in the center of the sheet 11 in the manner shown in FIGURE 2.

Unlike the line wave generators of the prior art, the present line wave generator is capable of generating a detonation front which is incident at the entire locus of the terminal edge 14 within 5 l08 seconds. This high degree of simultaneity is due to the combination of utilizing an explosive sheet 11 having a circular geometry wherein the distance from the ignition point to the terminal edge 14 is constant and piercing sheet 11 by radial cuts or slits which provide iiexibility associated with minimal strain upon deformation of the terminal edge 14. The ripple effect due to apertures which inhibit the progress of the detonation front is avoided by the manner in which the radial cuts are disposed, i.e., by rendering a central portion of the sector angularly discontinuous without the removal of any explosive material.

Any secondary curvature which the detonation front develops while traveling through one of the radial zones of the explosive sheet, e.g., as defined by radial cuts 12, is broken up and diminished as a result of the front encountering a second set of shorter radial cuts, e.g., cuts 16, piercing the zone to render it angularly discontinuous. Since the detonation frontlet is furthest advanced midway between said radial `cuts, it is preferred to subdivide the radial zones between said radial cuts by an uneven number of shorter cuts.

The simultaneity of the incidence of the detonation wave front at the terminal edge or locus may be further enhanced by providing a large number of radial cuts in close relationship to one another. On humping the central portion of the explosive sheet 11 to deform the terminal edge to some desired geometry, the edges of adjacent radial zones may remain in sufficiently close contact to allow communication in the form of cross ignition of the detonation wave across the radial cut. In this manner, i.e., by humping the center of the explosive sheet to dispose adjacent radial zones in close proximity to one another, the retarding effect of the explosive sheet boundary on the propagation of the detonation wave is reduced. The simultaneity with which the detonation wave front arrives at the terminal edge may be further enhanced by terminating the radial cuts at such a distance from the terminal edge that the proximity of said radial cuts to the terminal edge is inversely related to the length of the radial cuts.

An explosive sheet 11, having an apex angle of 55 and a radial length of 20 cm. was cut from `a section of rubber polymeric resin bonded pentaerythritol tetranitrate (PETN) explosive. (DuPont EL-506) The sector was slit to provide seven equally spaced radial cuts 12 beginning about 8 cm. from the apex 13 and terminating 4 about 5 mm. from the peripheral terminal edge 14. Beginning about 12.5 cm. from the apex 13 of a second set of 8 radial cuts 16 were made to bisect the radial zones defined by the first set of radial cuts 12. The second Set of radial cuts 16 also terminated about 5 mm. from the terminal edge 14. A third set of 16 radial cuts 17 was incised to bisect the radial zones defined by the first and second sets of cuts 12 and 16, respectively. The third set of cuts began about l5 cm. from the apex 13 and terminated about 5 mm. from the terminal edge 14. A fourth set of 32 radial cuts 18 about 2 cm. long `and terminating .about 5 mm. from the arcuate edge 14 as with the third set of cuts bisected the radial zones bounded by the third and first or second radial cuts 17, 12 and 16, respectively.

The line wave generator was found suitable for producing a straight line shock wave by humping the central region of the explosive sheet in the proximity of the terminal edge as shown in FIGURE 2. The detonation front was found to reliably arrive at the entire locus of the terminal edge 14 within 5 lO-B seconds.

The line wave generator of the present invention can be further adapted to simultaneously ignite geometric patterns of greater complexity by attaching the terminal edge to the locus of simultaneous ignition and deforming the explosive sheets into a surface characterized by minimal stress on the explosive sheet. It will be realized, however, that to simultaneously ignite any pattern requiring a greater explosive sheet surface deformation than that corresponding to the straight line terminal edge, it is necessary to increase the number of radial cuts in order to relieve the tension and strain on the explosive material. In all these applications, the cross section of the radial zones must, of course, be large enough to support the detonation. The minimum cross sectional area depends on the type of explosive used. For the explosive Piccolyte this minimum cross section is about 8 mm.z

It is obvious, therefore, that the number of individual radial cuts and the number of sets of radial cuts depends on the narrowness of the time interval during which ignition of the locus is desired, and the geometrical complexity of the locus. Accordingly, the scope of the invention is to be limited only by the following claims.

What is claimed is:

1. An explosive line wave generator comprising a sheet of flexible explosive having the shape of a circular sector, said sector being pierced by a multiplicity of sets of radial cuts, the cuts of each set being of uniform length, each of said sets of radial cuts at spaced locations beginning in proximity to the circular edge of the sector and converging generally along radii toward the apex of said sector, and each of said sets of radial cuts subdividing the radial zones defined by at least one other set of radial cuts.

2. The explosive line wave generator of claim 1 wherein said sets of radial cuts have progressively greater lengths.

3. The explosive line wave generator of claim 2 wherein shorter sets of radial cuts subdivide into equal radial zones, the radial zones defined by a set of radial cuts of greater length.

4. The explosive line wave generator of claim 3 wherein shorter sets of radial cuts subdivide into an even number of equal portions, the radial zones defined by a set of radial cuts of greater length.

5. An explosive line wave generator comprising a sheet of liexible explosive of uniform thickness and composition having the shape of a circular sector, said sector being pierced by a multiplicity of sets of radial cuts, said sets of cuts having a progressively greater length, said radial cuts beginning in spaced proximity to the circular edge of the sector, and each of said sets of radial cuts subdividing into an even number of equal portions, the radial zones defined by at least one other set of radial cuts.

6. The explosive line wave generator of claim 5 wherein shorter of said sets of radial cuts subdivide into two equal portions, the radial zones defined by a set of radial cuts of greater length.

7. The explosive line wave generator of claim 5 Wherein the proximity of sai-d radial cuts to said circular edge is inversely related to the length of the radial cuts.

8. The explosive line wave generator of claim 5 wherein the apex angle of said circular sector is acute.

9. The explosive line wave generator of claim 5 further dened by said radial zones of said explosive sheet being predeterminedly displaced with respect to the surface of adjacent radial zones whereby the terminal edge is deformed to assume a desired geometry, adjacent edges of said radial Zones .being separated by a distance supporting the communication of the detonation Wave between said radial zones.

1t). An explosive line wave generator comprising a sheet of exible explosive; said explosive being comprised of PETN, an organic rubber, and a thermoplastic terpene resin; said explosive being of uniform thickness and composition having the shape of a circular sector; said sector being pierced by a multiplicity of sets of radial cuts, said sets of cuts having a progressively greater length, said cuts beginning in proximity to the peripheral edge of said sector, the proximity of the radial cut to the terminal edge being inversely related to the length of the cuts, said sets of radial cuts lbisecting the radial Zones dened by the set of radial cuts of progressively greater length, and said peripheral edge of the sector being deformed to a straight edge, said radial zones being uniformly displaced normally to said sector in the central region thereof, adjacent edges of said radial zones separated by a distance supporting the communication of the detonation wave between said radial zones.

References Cited by the Examiner UNITED STATES PATENTS 2,774,306 12/1956 MacLeod.

2,943,571 7/1960 Coursen.

3,035,518 5/1962 Coursen lOZ-ZZ 3,169,478 2/1965 Schaaf 102-22 BENJAMIN A. BORCHELT, Primary Examiner.

R. V. LOTTMANN, Assistant Examiner. 

1. AN EXPLOSIVE LINE WAVE GENERATOR COMPRISING A SHEET OF FLEXIBLE EXPLOSIVE HAVING THE SHAPE OF A CIRCULAR SECTOR, SAID SECTOR BEING PIERCED BY A MULTIPLICITY OF SETS OF RADIAL CUTS, THE CUTS OF EACH SET BEING OF UNIFORM LENGTH, EACH OF SAID SETS OF RADIAL CUTS AT SPACED LOCATIONS BEGINNING IN PROXIMITY TO THE CIRCULAR EDGE OF THE SECTOR AND CONVERGING GENERALLY ALONG RADII TOWARD THE APEX OF SAID 